Database
[{"WorkspacePartTeamsite":{"SiteContents":[{"_id":"00000000-0000-0000-0000-000000000002","Name":"PublicFiles"},{"_id":"ad57fee3-e478-46a6-a8c1-499dcc98995f","Name":"Private"},/**...*/]}}]
Query
db.collection.update({},[{$set:{"WorkspacePartTeamsite.SiteContents":{$map:{input:"$WorkspacePartTeamsite.SiteContents",as:"item",in:{$mergeObjects:["$$item",{SPOSegment:"$$item.Name"}]}}}}}],{multi:true})